1. Field of the Invention
The present invention relates to a heating plate crystallization method used in the crystallization process for the poly-silicon thin-film transistor, and more particularly, to a heating plate crystallization method using a rapid thermal annealing process.
2. Description of the Prior Art
The prior art crystallization technology includes the solid phase crystallization technology and the excimer laser annealing (ELA) technology. Because the crystallization temperature required by the solid phase crystallization method (SPC) is about 600° C. and the deformation temperature of the glass substrate (Corning 1737) is about 666° C., the solid phase crystallization method (SPC) cannot be accomplished on a cheaper glass substrate, and a material with high price is required, such as quartz chip. The limitation over the material will cause the manufacture cost increased. When applying the excimer laser annealing (ELA) technology, although the temperature of the substrate for the crystallization process is lower than that of the solid phase crystallization method, the facility requirement of the ELA technology is relatively high. Therefore, the technology of the present invention provides a poly-silicon thin-film transistor having a structure of a heating plate area. By means of the special characteristic of the heating plate area, namely, the selective heating, the poly-silicon thin-film transistor can be crystallized under the status of high temperature, and the substrate will not be damaged. Therefore, the technology according to the present invention is suitable in the glass substrate, and the facility is inexpensive. This makes the inventive technology is highly valuable in the industry.
The prior art the metal induced lateral crystallization (MILC) method uses a heating tube to heat the seed deposited on the amorphous layer. Please refer to FIG. 1A to 1D show the flowchart of a prior art the metal induced lateral crystallization method. Please refer to FIG. 1A. In the first step of the prior art the metal induced lateral crystallization method, a amorphous layer 20 is formed on a glass substrate 10. Next, please refer to FIG. 1B, in the second step of the method, the metal, such as Ni, Pd, and so on, is deposited on the amorphous layer 20 by using the physical vapor depositing or electroplating method. Then, please refer to FIG. 1C. In the third step of the method, by using the lithography, etching processes, the local metal distribution is formed so as to advantage the following metal induced lateral crystallization (MILC) process. By the amorphous layer 20 and the metal thin-film deposited on the amorphous layer 20, the silicide 31 is formed. The silicide 31 can be used as the seed for the amorphous layer 20 to be crystallized so as to form the poly-silicon 32. The silicon molecules of the amorphous layer 20 can be melted by the silicide 31 so as to separate out the crystal. Please refer to FIG. 1D. In the final step of the prior art the metal induced lateral crystallization method, in the thermal annealing system, the metal induced lateral crystallization stage is performed so as to advance the amorphous layer 20 to be crystallized so as to form the poly-silicon 32. When the metal induced lateral crystallization (MILC) is occurred on the amorphous layer 20, the silicide formed by melting will spread to the non-defined amorphous layer. Therefore, the metal pollution will appear in the TFT device channel area so that the electric leakage of the TFT device will be increased and the electricity of the TFT device will be affected.
Therefore, in order to resolve the mentioned problems, the present invention provides a heating plate crystallization method used in the crystallization process for the poly-silicon thin-film transistor, and more particularly, the present invention relates to a heating plate crystallization method by using a rapid thermal annealing process. The difference between the inventive method and the metal induce lateral crystallization method is that the heating plate area provided by the inventive method will not be melted with the amorphous layer to form the silicide. Therefore, it is not to induce the lateral crystallization by using the silicide. In the present invention, the heating plate area has a better absorption rate to the infrared rays and a high thermal stability. By using the heating plate area to absorb the infrared rays, after the heating, the energy is indirectly transferred to the amorphous layer via a thermal conduction method so that the amorphous layer is rapidly crystallized to form the poly-silicon. Furthermore, a thin oxide layer is deposited between the heating plate area and the amorphous layer, and when using the oxide layer to stop the rapid thermal annealing process, the high thermal diffusion will occur between the heating plate area and the amorphous layer so as to effectively avoid the metal pollution in TFT device channel area. Furthermore, the present invention uses the pulsed rapid thermal annealing process (PRTP), using the infrared rays to instantly heat, to selectively heat the materials by taking the advantage that different materials have different absorption rates to the infrared rays. The glass substrate and the amorphous cannot effectively absorb the infrared rays so that the glass substrate will not be broken while the process temperature of the heating plate area is excessively high (>700° C.). Therefore, the most effective rapid thermal crystallization by HPC method can be achieved.